The need to protect an article, or a part thereof, from a hostile environment exists in many areas of technology and commerce. For instance, it is often necessary to protect electrical equipment or components against contact with water or moisture. A particular example of this is the need to so protect joints or splices between electrical conductors, e.g., splice points between multiconductor communications cables.
A frequently used technique for protecting such splice points comprises providing an enclosure around the completed splice, and introducing a curable or gelable liquid into the enclosure. The liquid should ideally fill all the voids between the conductors and other splice components and form closely adhering interfaces with all the surfaces it contacts within the enclosure, thereby reducing the possibility of water migration along such interfaces, which can result in water contact with conductors or other sensitive splice components.
An encapsulating compound for cable splices and the like should ideally also have other desirable characteristics, such as compatibility with all the materials it contacts, chemical stability over a wide range of operating temperatures, good electrical properties, be reenterable, nonsagging at high temperatures, retain acceptable mechanical properties at low temperatures, be nontoxic to personnel in both the liquid and the cured state, and be acceptable under applicable environmental laws.
Although no prior art encapsulating compound fully possesses all these desirable characteristics, splice encapsulants are in widespread use, in particular, in the telephone industry.
Among the currently most frequently used encapsulant are polyurethane-based material compositions mineral oil extended compositions. For instance, U.S. Pat. No. 4,168,258, issued Sept. 18, 1979 to M. Brauer et al, discloses a cured, cross-linked grease-compatible polyurethane-based material comprising mineral oil and a coupling agent, useful for sealing an insulated electrical device. See also U.S. Pat. No. Re. 30,321.
Similarly, U.S. Pat. No. 4,329,442, issued May 11, 1982 to R. J. Pokorny, discloses a polyurethane prepared from an aliphatic or cycloaliphatic isocyanate, a polydiol, a tri-or tetra-functional aliphatic polyol, a monofunctional aliphatic alcohol, and a catalyst, the composition being useful as an encapsulating compound, said to have good adhesion to greasy insulation material.
Prior art encapsulants, especially cable slice encapsulants, generally are formulated to have relatively short cure (gel) times. For instance, an encapsulant that has recently become available commercially is said to have a gel time of 20 minutes at 23.degree. C., and a gel time at -18.degree. C. of only 35 minutes. The art considers short gel time to be advantageous, since it reduces the time required to complete a splice, and allows speedy job completion.
Priort art encapsulants, which often have initial mixed viscosity in the order of 300-1500 cps (centipoise) at room temperature, tend to have rapidly increasing viscosities, due to their short cure time. This sometimes results in poor penetration of encapsulant into the splice bundle.
The prior art knows compounds, useful in rehabilitation of water-logged cable, that have very low initial mixed viscosity (e.g., about 100 cps at 35.degree. F., about 10 cps at room temperature) and long cure time. See, for instance, U.S. Pat. No. 3,733,426. Such compounds typically are not useful as splice encapsulants, due to their tendency to stress crack polycarbonate.
Although widely used, prior art cable splice encapsulation systems do not provide fully satisfactory protection against water intrusion into the splice work, and the resulting damage and deterioration of service. As a consequence, there exists a need for a splice system that retains the important advantages of prior art systems while, at the same time, being capable of giving improved protection against water intrusion. This application discloses encapsulants having novel properties that result in improved water intrusion resistance. U.S. patent application Ser. No. 619,266 filed June 11, 1984, co-assigned with this, and incorporated herein by reference, discloses a forced encapsulation system in which the instant encapsulant can be advantageously used.